Like many computer related electronics, consumer driven innovations fueled by an insatiable thirst for data storage has diversified an expanding storage industry. This is exemplified by the variety of disc drive storage array systems which are among the many mass storage options available. Disc drive storage arrays are gaining popularity due to the many advances in disc drive technology such as high areal density with a consumer-friendly cost structure and ever faster speeds at which data are storable and retrievable. High disc drive storage speeds have, in turn, necessitated innovations including ways in which data are piped to and from the drives. Such innovations include data paths and protocols such as Serial Advanced Technology Attachment (SATA) used for low cost desktop environments, parallel Small Computer System Interface (SCSI) and Serial Attached SCSI (SAS) used for high performance enterprise environments which include disc drive storage arrays, just to name three examples.
Generations of SAS disc drives have the advantage of parallel SCSI robustness with the added benefit of significantly expanding the SCSI envelope in terms of speed, scalability and flexibility thanks, in part, to recent advancements in Very Large Scale Integration technology. Furthermore, SAS systems have remarkable scalability relative to parallel SCSI systems, made possible by the multiple low-cost switches that comprise an SAS expander. For example, each SAS expander may enable 128 point-to-point connections that, when coupled with additional expanders, such as off of a Host Bus Adapter (HBA), may be able to aggregate thousands of devices while preserving performance and reliability. By contrast, parallel SCSI has an imposed limit of fifteen devices per SCSI chain and limits to total cable length.
In the event additional SAS drives are needed beyond the capacity of the HBA, additional HBAs can be connected to the storage array system bus, often a Peripheral Computer Interface (PCI) bus (most motherboards for a storage array system have at least multiple 32 bit and 64 bit edge connectors). Additional HBAs connected to the main storage array system bus not only have the disadvantage of consuming additional bandwidth, but are expensive. One standard solution is to provide a back plane of a library system, however, this solution requires additional electronics and requires additional accommodating library space.
In an effort to expand data to peripherals beyond the original intent of an HBA while reducing the dependency of a back plane device and coincidentally taking advantage of the geometric layout of a standard PCI bus, solutions drawn to both methods and apparatus are disclosed herein. It is to innovations related to this subject matter that the claimed invention is generally directed.